Oceanography in the mid-20th century was "one of the greatest
periods of exploration of the earth ... Every time you went to
sea, you made unexpected discoveries. It was revolutionary.
Nothing that we expected was true. Everything we didn't expect
was true."

This striking declaration comes from Roger Revelle, the U.S.
Navy's chief oceanographer during World War II and the man
responsible for transforming the Scripps Institution of
Oceanography in La Jolla, California into a major research
institution, leading major expeditions to the Mid- and
South-Pacific in 1950 and 1952 (as quoted in Daniel Yergin's
"The
Quest: Energy, Security and the Remaking of the Modern
World").

What oceanographers realized was that the deep-sea floor was not
a flat and featureless plan but rather a dynamic landscape with
vast mountain ranges, deep basins, and long trenches. Although
this understanding had been developing for centuries, the real
breakthroughs came after World War II.

In the 1950s oceanic explorations greatly expanded. Data gathered
by oceanographers from many countries led to the discovery of a
great mountain range on the ocean floor virtually encircling the
Earth.

Known as the global mid-ocean ridge, this immense submarine
mountain chain more than 50,000 kilometers long and in places
more that 800 kilometers across zigzags between the continents
winding its way around the globe like a seam on a baseball.
Though hidden beneath the ocean surface, the global mid-ocean
system is the most prominent topographic feature on the surface
of the planet.

The results from the first measurements of heat flow through the
sea floor were among several surprises gathered on the first
major Scripps expedition, Midpac, in 1950: the temperature
gradient was very similar to that measured on lean, whereas it
had been expected to be considerably less. "The only adequate
source of heat that has been suggested is radioactivity within
the earth," noted Bullard, and oceanic basalts are considerably
less radioactive than continental rocks. The source of heat,
therefore, must be deeper within the earth, presumably beneath
the Mohorovičić discontinuity.

They also discovered unexpected magnetic patterns on the sea
floor, per Shor:

The chart of magnetic intensities from the Pioneer survey
startled geologists. Before them lay evidence of great
north-south lineations and a single right-lateral offset of 155
kilometers along the Murray fracture zone off southern
California. The survey was "the first attempt to make a detailed
magnetic map of an extensive area of the oceans," said Bullard
and Mason. "The results are of exceptional interest in that they
reveal major structural trends of which there is little or no
indication in the topography, and they provide evidence for
unsuspected horizontal displacements along some of the faults of
the north-east Pacific greater than any that have so far been
observed over the continents."

From these and other breakthroughs came a radical
re-understanding of plate tectonics, per USGS:

In 1961, scientists began to theorize that mid-ocean ridges mark
structurally weak zones where the ocean floor was being ripped in
two lengthwise along the ridge crest. New magma from deep with
the Earth rises easily through these weak zones and eventually
erupts along the crest of the ridges to create new oceanic crust.
...

[H]ow could new crust be made and continuously added along the
ridges without increasing the size of the Earth? The question
intrigued Harry H. Hess, a Princeton University geologist, and
Robert S. Dietz, a scientist with the U.S. Coast and Geodetic
Survey. Dietz and Hess coined the expression seafloor spreading.
They understood the broad implications of this phenomenon. If the
Earth's crust was expanding along the oceanic ridges, it must be
shrinking elsewhere. Hess suggested that the new oceanic crust
continuously moves away from the ridges' conveyor belt-like
motion. Millions of years later, the oceanic crust descends into
oceanic trenches. As old crust was consumed in the trenches, new
magma rose and erupted along the spreading ridges to form new
crust. In effect, the ocean basics were perpetually being
"recycled" with the creation of new crust and the destruction of
old oceanic lithosphere occurring simultaneously. According to
Hess, the Atlantic was expanding and the Pacific shrinking.

The continents, which are lighter than the ocean crust, glide
over the surface of the Earth in response to the expansion and
contraction along oceanic ridges. They are carried along as the
ocean floor spreads from the ridges.

A better understanding of the oceans, which cover 71% of Earth's
surface, as well as the tectonic processes that shape our planet
would prove useful in many fields. Perhaps most importantly, it
began to unlock
the study of climate change and the role that humans would
play by
increasing the buildup of carbon dioxide in the atmosphere,
what Revelle called, "a large scale geophysical experiment of a
kind that could not have happened in the past nor be reproduced
in the future."

Not only were these discoveries incredibly important, but being
an oceanographer in this heady climate sounds fun, too.

That much is obvious in an account
by Edward S. Barr of how after his junior year of high school
in San Diego he convinced Revelle to take him on the 1950 MidPac
expedition as a $75-a-month lab assistant, and how they traveled
to Honolulu, the Marshall Islands, the Kwajalein Atoll, and deep
into the South Pacific, with prolific discoveries and adventure
all the way.

One photo included in the memoir, which shows Barr using a
fathometer echo sounder on August 31, 1950, is labeled:
"Discovering the MidPac Mountain Range on my watch!"